3.II.6D

Let $\mathcal{M}$ be the group of Möbius transformations of $\mathbb{C} \cup\{\infty\}$ and let $S L(2, \mathbb{C})$ be the group of all $2 \times 2$ complex matrices with determinant 1 .

Show that the map $\theta: S L(2, \mathbb{C}) \rightarrow \mathcal{M}$ given by

$\theta\left(\begin{array}{ll} a & b \\ c & d \end{array}\right)(z)=\frac{a z+b}{c z+d}$

is a surjective homomorphism. Find its kernel.

Show that every $T \in \mathcal{M}$ not equal to the identity is conjugate to a Möbius map $S$ where either $S z=\mu z$ with $\mu \neq 0,1$, or $S z=z \pm 1$. [You may use results about matrices in $S L(2, \mathbb{C})$, provided they are clearly stated.]

Show that if $T \in \mathcal{M}$, then $T$ is the identity, or $T$ has one, or two, fixed points. Also show that if $T \in \mathcal{M}$ has only one fixed point $z_{0}$ then $T^{n} z \rightarrow z_{0}$ as $n \rightarrow \infty$ for any $z \in \mathbb{C} \cup\{\infty\} .$

*Typos? Please submit corrections to this page on GitHub.*